Surface-modified colloidal silica and polishing composition containing the same

Abstract

The surface-modified colloidal silica of the present invention comprises: colloidal silica, and a surface-modifying group having a polyoxyethylene chain having a weight average molecular weight of 20,000 or more on the surface of the aforementioned colloidal silica.

Description

[Technical Field]

[0001] This invention relates to surface-modified colloidal silicon dioxide and grinding compositions containing the same. [Previous Technology]

[0002] In recent years, with the increasing use of multilayer wiring on the surface of semiconductor substrates, chemical mechanical polishing (CMP) technology, which involves planarizing semiconductor substrates by grinding them, has been employed in manufacturing equipment. CMP is a method of planarizing the surface of a workpiece (the object being polished), such as a semiconductor substrate, using a polishing composition (slurry) containing abrasive particles such as silicon dioxide, aluminum oxide, or cerium oxide, as well as a etching inhibitor and a surfactant. Specifically, it is used in steps such as shallow trench separation (STI), planarization of interlayer insulating films (ILD films), tungsten plug formation, and formation of multilayer wiring made of copper and low-dielectric films. For example, Japanese Patent Application Publication No. 2009-256184 discloses colloidal silicon dioxide surface-modified with polycyclohexane with a molecular weight of 15,000 or less and a polishing composition for CMP containing the same. [Summary of the Invention]

[0003] However, in the technology disclosed in Japanese Patent Application Publication No. 2009-256184, the abrasive composition has low wettability to the workpiece being abraded, resulting in insufficient improvement in abrasive performance by maintaining the surface condition of the workpiece well and / or achieving an appropriate abrasive speed. Furthermore, in the technology disclosed in Japanese Patent Application Publication No. 2009-256184, the dispersibility of surface-modified colloidal silica decreases over time, resulting in insufficient stability over time. Therefore, the object of the present invention is to provide a means to improve wettability and stability over time for abrasive workpieces made of surface-modified colloidal silica. To solve the above problems, the inventors have repeatedly and diligently conducted research. As a result, it was found that the above-mentioned problems could be solved by using a surface-modified colloidal silica, which comprises colloidal silica and a surface-modifying group having a polyoxyethylene chain with a weight average molecular weight of 20,000 or more to modify the colloidal silica, and the present invention was finally completed.

Implementation Method

[0004] [Forms of the Invention] Hereinafter, embodiments of the present invention will be described. Throughout this specification, the singular form, unless specifically stated otherwise, should be understood to include the concept of its plural form. Therefore, articles in the singular form (e.g., "a," "an," "the," etc. in English), unless specifically stated otherwise, should be understood to include the concept of its plural form. Furthermore, the terms used in this specification, unless specifically stated otherwise, should be understood to be used in the meaning commonly used in the field. Therefore, unless otherwise defined, all specialized and scientific terms used in this specification have the same meaning as generally understood by those skilled in the art to which this invention pertains. In case of conflict, this specification (including definitions) shall prevail. Furthermore, the present invention is not limited to the embodiments described below. Furthermore, in this specification, unless specifically stated otherwise, the measurement of operation and physical properties, etc., is carried out under conditions of room temperature (20°C to 25°C) and relative humidity of 40%RH to 50%RH. One embodiment of the present invention comprises a surface-modified colloidal silica comprising: colloidal silica, and a surface-modifying group having a polyoxyethylene chain having a weight average molecular weight of 20,000 or more, which modifies the aforementioned colloidal silica. By having such a configuration, the surface-modified colloidal silica of one embodiment of the present invention improves wettability to the workpiece being polished and enhances stability over time. [Surface-modified colloidal silica] (colloidal silica) Methods for manufacturing the colloidal silica contained in the surface-modified colloidal silica of one embodiment of the present invention include the sodium silicate method and the sol-gel method; colloidal silica manufactured by any of these methods is applicable to the present invention. However, from the viewpoint of reducing metallic impurities, colloidal silica manufactured by the sol-gel method is preferred. Colloidal silicon dioxide manufactured by the sol-gel method is preferable because it contains less diffusible metallic impurities or corrosive ions such as chloride ions in semiconductors. The manufacture of colloidal silicon dioxide by the sol-gel method can be carried out using conventional methods. Specifically, colloidal silicon dioxide can be obtained by hydrolyzing and condensing a hydrolyzable silicon compound (e.g., alkoxysilanes or their derivatives) as a raw material. The lower limit of the average primary particle size of the colloidal silicon dioxide is preferably 1 nm or more, more preferably 5 nm or more, and particularly preferably 7 nm or more. Furthermore, the upper limit of the average primary particle size of the colloidal silicon dioxide is preferably 100 nm or less, more preferably 75 nm or less, and particularly preferably 50 nm or less. Within this range, defects such as scratches that may occur on the surface of the object being polished after polishing with polishing compositions can be suppressed. That is, the average primary particle size of colloidal silicon dioxide is preferably 1 nm to 100 nm, more preferably 5 nm to 75 nm, and even more preferably 7 nm to 50 nm.Furthermore, the average primary particle size of colloidal silica is calculated, for example, based on the specific surface area of ​​colloidal silica determined by the BET method. The lower limit of the average secondary particle size of colloidal silica is preferably 2 nm or more, more preferably 10 nm or more, and particularly preferably 15 nm or more. Furthermore, the upper limit of the average primary particle size of colloidal silica is preferably 200 nm or less, more preferably 150 nm or less, and particularly preferably 100 nm or less. That is, the average secondary particle size of colloidal silica is preferably 2 nm or more and 200 nm or less, more preferably 10 nm or more and 150 nm or less, and particularly preferably 15 nm or more and 100 nm or less. Furthermore, the average secondary particle size of colloidal silica can be determined, for example, by dynamic light scattering methods such as laser diffraction scattering. The average binding density of colloidal silica is preferably 5.0 or less, more preferably 4.0 or less, and particularly preferably 3.0 or less. This can further reduce defects. Furthermore, the average bonding strength of the colloidal silica is preferably 1.0 or higher, more preferably 1.2 or higher, and even more preferably 1.5 or higher. That is, the average bonding strength of the colloidal silica is preferably 1.0 or higher and 5.0 or lower, more preferably 1.2 or higher and 4.0 or lower, and even more preferably 1.5 or higher and 3.0 or lower. The average bonding strength is obtained by dividing the average secondary particle size of the colloidal silica by the average primary particle size. The shape of the colloidal silica is not particularly limited; it can be spherical or non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular or quadrangular prisms, cylindrical shapes, straw-bag-like shapes where the central part of a cylinder is more bulging than the ends, donut-like shapes penetrating the central part of a disc, plate-like shapes, so-called cocoon-like shapes with a constricted neck in the central part, so-called combined spherical shapes where multiple particles are integrated, konpeito shapes with multiple protrusions on the surface, rugby ball shapes, and various other shapes, without particular limitation. [Surface Modification Group with Polyoxyethylene Chain] One embodiment of the present invention has a surface-modified colloidal silica with a surface modification group. The surface modification group of the present invention is a group having a polyoxyethylene chain with a weight average molecular weight of 20,000 or more. Examples of the aforementioned polyoxyethylene chain include polyethylene glycol chains, polypropylene glycol chains, polytrimethylene glycol chains, polytetramethylene glycol chains, polyisobutylene glycol chains, etc. In the surface-modifying group of the present invention, the aforementioned polyoxyethylene chain may be composed of only one type of olefin oxide, or it may be composed of two or more types of olefin oxide. Examples of polyoxyethylene chains composed of two or more types of olefin oxide include polyoxyethylene-polyoxypropylene chains, polyoxyethylene-polyoxytetramethylene chains, and polyoxyethylene-polyoxypropylene-polyoxyethylene chains. When the surface-modifying group of the present invention is composed of two or more types of olefin oxide, the bonding morphology of the two or more olefin oxides may be random, alternating, block, or periodic. Preferably, it is selected from at least one type selected from the group consisting of polyoxyethylene chains, polyoxypropylene chains, polyoxyethylene-polyoxypropylene chains, and polyoxyethylene-polyoxypropylene-polyoxyethylene chains, and more preferably, it is a polyoxyethylene chain.One embodiment of the present invention has a surface-modifying group having a structure in which the ends of a polyoxyethylene chain are closed by an aliphatic hydrocarbon group. That is, the hydrogen atom in the hydroxyl group at the end of one polyoxyethylene chain can be replaced by an aliphatic hydrocarbon group. Examples of aliphatic hydrocarbon groups closing the ends of the aforementioned polyoxyethylene chain include aliphatic hydrocarbon groups having 1 to 10 carbon atoms. Examples of aliphatic hydrocarbon groups having 1 to 10 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, dibutyl, tributyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, and decyl; linear or branched alkenyl groups such as vinyl and allyl; and alkynyl groups such as ethynyl and propynyl. Among these, linear or branched alkyl groups are preferred. In one embodiment of the present invention, the polyoxyethylene chain in the surface-modifying group has a weight-average molecular weight (Mw) of 20,000 or more. When the weight-average molecular weight of the polyoxyethylene chains is less than 20,000, the wettability decreases. Furthermore, to obtain the desired properties, more surface modifiers must be added during synthesis, resulting in a decrease in the stability of the surface-modified colloidal silica over time. There is no particular upper limit to the weight-average molecular weight of the polyoxyethylene chains, but it is preferably below 100,000, more preferably below 50,000. That is, the weight-average molecular weight of the polyoxyethylene chains is preferably between 20,000 and 100,000, more preferably between 20,000 and 50,000. Moreover, the weight-average molecular weight of the polyoxyethylene chains can be determined by gel permeation chromatography (GPC) using polyethylene glycol as a standard. Furthermore, in one embodiment of the present invention, the surface-modifying base preferably comprises silicon atoms and a linking base, and more preferably at least one base selected from the group consisting of the base shown in formula (1), the base shown in formula (2), and the base shown in formula (3). The wavy bonds in formulas (1) to (3) are bonded to the surface of colloidal silicon dioxide. In the above formulas (1) to (3), R1 independently represents a hydrogen atom or a hydrocarbon group with 1 to 30 carbon atoms, R2 independently represents an alkyl group, n independently represents the average degree of polymerization (number average degree of polymerization) of the oxidized olefin chain [-(O-R2)-], which is 280 or more, X independently represents a single bond or a linking group (a divalent group with 1 or more atoms), R3 and R4 independently represent a hydrogen atom, an aliphatic hydrocarbon group with 1 to 3 carbon atoms or the group shown in the following formula (a), in the above formula (a), RA represents [-X-(O-R2)n-OR1], in which case X, R1, R2 and n in RA are the same as X, R1, R2 and n defined in the above formulas (1) to (3), R5 and R6 independently represent a hydrogen atom or an aliphatic hydrocarbon group with 1 to 3 carbon atoms, and l and m independently represent a number of 0 or more. Furthermore, in equation (a), the bond system extending to the left from the silicon atom bonds to the oxygen atom.The wavy bond in formula (a) is bonded to the surface of colloidal silicon dioxide. Examples of alkyl groups with 1 to 30 carbon atoms used in R1 in formulas (1) to (3) above include methyl, ethyl, propyl, isopropyl, n-butyl, dibutyl, tributyl, isobutyl, pentyl, isopentyl, tripentyl, n-hexyl, cyclohexyl, cyclohexylmethyl, 2-cyclohexylethyl, n-heptyl, isoheptyl, triheptyl, n-octyl, isooctyl, trioctyl, 2-ethylhexyl, n-nonyl, isononyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecanyl, n-hexadecyl, n-heptadecyl, n-heptadecyl, n-heptadecyl, n-heptadecyl, n-octadecyl, etc.; vinyl, 1-methylvinyl, 2-methylvinyl, propenyl, butenyl, isobutylenyl, pentenyl, hexenyl, heptenyl, octenyl, decenyl, pentadecenyl, 1-phenylpropenyl, etc. Alkyl groups such as 3-ene; alkylaryl groups such as phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, 3-isopropylphenyl, 4-isopropylphenyl, 4-butylphenyl, 4-isobutylphenyl, 4-tert-butylphenyl, 4-hexylphenyl, 4-cyclohexylphenyl, 4-octylphenyl, 4-(2-ethylhexyl)phenyl, 4-stearylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl, 2,6-dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl, 2,4-ditert-butylphenyl; arylalkyl groups such as benzyl, phenethyl, 2-phenylpropane-2-yl, diphenylmethyl, triphenylmethyl; and arylalylalkenyl groups such as styryl and cinnamyl. In the above formulas (1) to (3), R2 represents an alkyl group, preferably an alkyl group having 1 to 4 carbon atoms. Examples of alkyl groups with 1 to 4 carbon atoms include methylene, ethyl, propyl (methyl ethyl), trimethylene, butyl (tetramethylene), and isobutyl. Among these, ethyl and propyl are preferred. The plurality of R2s may be the same or different. When the plurality of R2s are different, the bonding morphology of the above-mentioned oxidized olefin chain [-(O-R2)-] may be random, alternating, block, or periodic. In the above formulas (1) to (3), n is the average degree of polymerization (number average degree of polymerization) of the oxidized olefin chain [-(O-R2)-], which is a number of 280 or more. n is preferably a number of 345 to 1725, and more preferably a number of 455 to 1390. When n is 280 or more, the steric barrier between the surface-modifying groups of the present invention becomes sufficient, making it easy to disperse in the dispersion medium and exhibiting good wettability to the object being ground. In formulas (1) to (3) above, X represents a single bond or a linking group (a divalent group having one or more atoms). Examples of such linking groups include divalent hydrocarbon groups, aminoformate bonds, carbonyl groups, ether bonds, ester bonds, carbonate groups, amide groups, and groups formed by the linkage of one or more of these. Examples of such divalent hydrocarbon groups include linear, branched, or cyclic alkyl groups having 1 to 18 carbon atoms.Examples of linear, branched, or cyclic alkyl groups having 1 to 18 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethyl alkyl, propyl alkyl (methyl ethyl alkyl), trimethylene, butyl alkyl (tetramethylene), 1-methylpropyl alkyl, 2-methylpropyl alkyl, 1,2-dimethylpropyl alkyl, 1,3-dimethylpropyl alkyl, 1-methylbutyl alkyl, 2-methylbutyl alkyl, 3-methylbutyl alkyl, 2,4-dimethylbutyl alkyl, 1,3-dimethylbutyl alkyl, n-pentyl alkyl, n-hexyl alkyl, n-heptyl alkyl, n-octyl alkyl, ethane-1,1-diyl, propane-2,2-diyl alkyl Cyclocyclohexane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl, octadecane-1,18-diyl, cyclopentane-1,2-diyl, cyclopentane-1,3-diyl, cyclohexane-1,1-diyl, cyclohexane-1,2-diyl, cyclohexane-1,3-diyl, cyclohexane-1,4-diyl, methylcyclohexane-1,4-diyl, cyclohexane-1,4-dimethylene, etc. As the linking group in X above, from the perspective of ease of synthesis, it is preferable to include an aminocarbamate bond, and more preferably to include a divalent hydrocarbon group (especially a straight-chain or branched alkyl group) and an aminocarbamate bond. Furthermore, the silicon atom in formulas (1) to (3) above is preferably directly bonded to the divalent hydrocarbon group (especially a straight-chain or branched alkyl group) in X. Specifically, X is more preferably -(CH2)k-NH-C(=O)- (the C on the left is bonded to the silicon atom, and the C on the right is bonded to the O in the polyoxyalkylene chain). Moreover, in the above formulas, k represents a number of 1 to 18, preferably 1 to 6, and more preferably 1 to 3. In formula (1) above, R3 and R4 each independently represent a hydrogen atom or an aliphatic hydrocarbon group with 1 to 3 carbon atoms. Examples of aliphatic hydrocarbon groups with 1 to 3 carbon atoms include alkyl groups such as methyl, ethyl, propyl, and isopropyl; alkenyl groups such as vinyl and allyl; and alkynyl groups such as ethynyl and propynyl. Alkyl groups are preferred. Furthermore, R3 in formula (2) is the same as R3 in formula (1). In formula (a) above, RA represents [-X-(O-R2)n-OR1]. X, R1, R2, and n in RA are the same as those exemplified and described in formulas (1) to (3) above, and the preferred state is also the same. Furthermore, the bonding morphology when there are two or more oxidized alkene chains [-(O-R2)-] is also as described above. Furthermore, the bond system extending to the left from the silicon atom is bonded to the oxygen atom. The bond system with wavy lines in the formula is bonded to the surface of colloidal silicon dioxide. In the above formula (a), R5 and R6 each independently represent a hydrogen atom or an aliphatic hydrocarbon group with 1 to 3 carbon atoms.Examples of aliphatic hydrocarbon groups with 1 to 3 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, n-propyl, and isopropyl; linear or branched alkenyl groups such as vinyl, allyl, and propenyl; and alkynyl groups such as ethynyl and propynyl. Among these, linear or branched alkyl groups are preferred. In formula (a) above, l and m each independently represent a number of 0 or more. The bonding order of the constituent units with l and the constituent units with m is not particularly limited. That is, the silicon atom in formula (a) bonded to the oxygen atom in formula (1) or (2) can be either a silicon atom in the constituent unit with l or a silicon atom in the constituent unit with m. Similarly, the oxygen atom in formula (a) bonded to R6 in formula (a) can be either an oxygen atom in the constituent unit with l or an oxygen atom in the constituent unit with m. Furthermore, when one of l and m is 1 or more, and the other is 2 or more, the bonding morphology of the constituent unit with l and the constituent unit with m can be any of random, alternating, block, or periodic. In one embodiment of the present invention, the surface-modified colloidal silicon dioxide, when having a plurality of R1 to R6, X, l, m, or n, can have the same or different numbers of R1 to R6, X, l, m, and n. Moreover, in formulas (1) and (2) above, the structures of R3 and R4 representing hydrogen atoms indicate a structure in which the unreacted alkoxysilyl group in the surface-modified group of the present invention bonded to colloidal silicon dioxide has undergone hydrolysis. Furthermore, the structures of R3 and R4 representing aliphatic hydrocarbon groups with 1 to 3 carbon atoms indicate a structure in which the unreacted alkoxysilyl group remains in the surface-modified group of the present invention bonded to colloidal silicon dioxide. Furthermore, R3 and R4 are the structures of the base shown in formula (a) above, representing structures in which the unreacted alkoxysilyl group in the surface-modified base of the present invention, which is bonded to colloidal silica, reacts with the unreacted silane coupling agent containing polyoxyolefin chains described later and / or colloidal silica, which are bonded by dehydration condensation, to other alkoxysilyl groups in the surface-modified base of the present invention. [Method for Manufacturing Surface-Modified Colloidal Silicon Dioxide] The method for manufacturing surface-modified colloidal silicon dioxide according to one embodiment of the present invention is not particularly limited. Examples include: (a) a method of pre-synthesizing a silane coupling agent containing a polyoxyethylene chain using a silane coupling agent having a group that can react with the terminal hydroxyl groups of a polyoxyethylene with a weight average molecular weight of 20,000 or more, and then reacting it with colloidal silicon dioxide; (b) a method of reacting a silane coupling agent having a group that can react with the terminal hydroxyl groups of a polyoxyethylene with a weight average molecular weight of 20,000 or more with colloidal silicon dioxide, and then further reacting a polyoxyethylene with a weight average molecular weight of 20,000 or more. From the viewpoint of easier reaction control and reduced manufacturing costs, method (a) is preferred. The method of (a) will be described in detail below.<Steps for Synthesizing a Silicon Coupling Agent Containing Polyoxyethylene Chains> In this step, a silicon coupling agent having a group capable of reacting with the terminal hydroxyl groups of a polyoxyethylene is reacted with a polyoxyethylene having a weight average molecular weight of 20,000 or more to synthesize a silicon coupling agent containing polyoxyethylene chains (hereinafter also referred to as "surface modifier"). There are no particular limitations on the silicon coupling agent having a group capable of reacting with the terminal hydroxyl groups of the polyoxyethylene, but it is preferred to use a silicon coupling agent containing isocyanate groups. Examples of silicon coupling agents containing isocyanate groups include 3-isocyanate propyltrimethoxysilane, 3-isocyanate propyldimethoxymethylsilane, 3-isocyanate propyltriethoxysilane, isocyanate methyltrimethoxysilane, isocyanate methyltriethoxysilane, and isocyanate methyldimethoxymethylsilane. These silane coupling agents can be used alone or in combination of two or more. Furthermore, these silane coupling agents can be commercially available or synthetic. There are no particular limitations on the polyoxyethylene with a weight average molecular weight of 20,000 or more; examples include polyethylene oxide, polypropylene oxide, polyoxybutene, polytetrahydrofuran, polyethylene oxide-polypropylene oxide diblock copolymers, polypropylene oxide-polytetrahydrofuran diblock copolymers, and polyethylene oxide-polypropylene oxide-polyoxyethylene triblock copolymers. Moreover, the bonding morphology of the copolymer can be random, alternating, block, or periodic. These polyoxyethylenes can be used alone or in combination of two or more. Furthermore, these polyoxyethylenes can be commercially available or synthetic. From the viewpoint of easily obtaining the effects of the present invention, polyethylene oxide is preferred among these polyoxyethylenes. There are no particular limitations on the reaction between the above-mentioned silane coupling agent and the polyoxyethylene; for example, it can be carried out in a solvent-free or organic solvent. Examples of usable organic solvents include aliphatic hydrocarbons such as hexane, heptane, and octane; aromatic hydrocarbons such as benzene, toluene, and xylene; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; aprotic polar solvents such as dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; halogenated hydrocarbons such as chloroform, dichloromethane, dichloroethane, carbon tetrachloride, chlorobenzene, and trifluoromethylbenzene; chain or cyclic ethers such as diethyl ether, diisopropyl ether, dimethoxyethane, tetrahydrofuran (THF), and dialkyl; esters such as ethyl acetate and butyl acetate; chain ketones such as methyl ethyl ketone (MEK) and methyl isobutyl ketone; and nitriles such as acetonitrile. Surface modifiers are obtained by mixing a silane coupling agent with polyoxyethylene. A preferred mixing method is to add a silane coupling agent to the polyoxyethylene and then mix. Regarding the form in which the silane coupling agent is added, it can be added in batches, in stages, or continuously. The addition rate can be adjusted appropriately when adding continuously. If the polyoxyethylene is in solid form, it can be heated before mixing to liquefy it before mixing. There are no particular limitations on the stirring speed during mixing; it can be set appropriately.The mixing time is preferably 15 minutes to 2 hours. The reaction temperature after mixing is preferably 20°C to 200°C, more preferably 50°C to 150°C. Furthermore, the reaction time after mixing is preferably 1 hour to 50 hours, more preferably 2 hours to 30 hours. The reaction environment can be, for example, any of air, nitrogen, argon, or other inert gas environments. Regarding the reaction pressure, it can be any of atmospheric pressure, under pressure, or under reduced pressure; there are no particular limitations. From the perspective of being able to carry out the reaction at atmospheric pressure, it is preferable to carry out the reaction at atmospheric pressure. The molar ratio of the silane coupling agent to the polyoxyethylene (silane coupling agent / polyoxyethylene) is preferably 0.5 to 1.5. In this way, the surface modifier of the present invention can be obtained. The structure of the obtained surface modifier can be confirmed, for example, by measuring the infrared absorption spectrum using the total reflectance method (ATR method) of a Fourier transform infrared spectrophotometer (FT-IR). Details of this method are described in the examples. After this step, the surface modifier can be isolated and purified, but it is also possible to proceed without isolation and purification, and instead perform the following step (the step of reacting colloidal silica with the surface modifier). <Step of reacting colloidal silica surface modifier> This step involves reacting the surface modifier obtained above with colloidal silica to obtain the surface-modified colloidal silica of the present invention. The colloidal silica has silanol groups on its surface, which serve as reaction sites, forming siloxane bonds with the surface modifier. The surface modifier (a silane coupling agent containing polyoxyalkylene chains) is preferably a compound represented by the following formula (1'). This surface modifier can be used alone or in combination of two or more. In the above formula (1'), R1, R2, X, and n are each the same as those exemplified and described in formulas (1) to (3) above, and the preferred forms are also the same. When using two or more compounds represented by the above formula (1'), the plurality of R1, R2, X, and n may each be the same or different. In the above formula (1'), R7 each independently represents an aliphatic hydrocarbon group having 1 to 3 carbon atoms. Examples of aliphatic hydrocarbon groups having 1 to 3 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, propyl, and isopropyl; linear or branched alkenyl groups such as vinyl, allyl, and propynyl; and alkynyl groups such as ethynyl and propynyl. Among these, linear or branched alkyl groups are preferred. This step is preferably carried out in a solvent. Examples of such solvents include water and / or the organic solvents exemplified above (in the step of synthesizing a silane coupling agent containing polyoxyalkylene chains). The solvent can be used alone or in combination of two or more. The mixed solution containing colloidal silica, surface modifier, and solvent is reacted in a reaction vessel with stirring. The colloidal silica and surface modifier used in the reaction are appropriately selected according to the desired degree of surface modification.As an example of the ratio of colloidal silica to surface modifier, the amount of surface modifier used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of colloidal silica. There are no particular limitations on the mixing method of colloidal silica and surface modifier, but a method of adding the surface modifier to colloidal silica and mixing is preferred. In this case, the colloidal silica can be added in batches, in portions, or continuously. There are no particular limitations on the stirring speed during mixing, and it can be set appropriately. The reaction temperature is preferably 20°C to 200°C, more preferably 30°C to 150°C. Furthermore, the reaction time is preferably 1 hour to 50 hours, more preferably 2 hours to 30 hours. The reaction environment can be, for example, any of an air environment, a nitrogen environment, an argon environment, or an other inert gas environment. Regarding the reaction pressure, it can be any of atmospheric pressure, under pressure, or under reduced pressure, without particular limitation. From the perspective of being able to carry out the reaction at atmospheric pressure, it is preferable to carry out the reaction at atmospheric pressure. As described above, a surface-modified colloidal silica according to one embodiment of the present invention is obtained. When the obtained surface-modified colloidal silica contains a dispersion medium other than water, the dispersion medium other than water can be replaced with water as needed. There is no particular limitation on replacing the dispersion medium other than water with water; for example, a method in which water is added dropwise while heating the surface-modified colloidal silica can be cited. Alternatively, a method in which the surface-modified colloidal silica is separated from the dispersion medium other than water by precipitation, separation, centrifugation, etc., and then redispersed in water can also be cited. The method for manufacturing the surface-modified colloidal silica according to one embodiment of the present invention may further include other steps. Examples of other steps include filtering a dispersion containing surface-modified colloidal silica, mixing a dispersion containing surface-modified colloidal silica with other additives (preferably a pH adjuster), and further filtering a dispersion containing surface-modified colloidal silica after mixing with other additives. The structure of the surface-modified colloidal silica of the present invention can be confirmed, for example, by detecting the T2 component (in the form of formula (2) above) or the T3 component (in the form of formula (3) above) using 29Si-NMR. In this specification, T refers to a Si atom that has 3 bonds bonded to O atoms and 1 bond bonded to polyoxyethylene chains, and the numbers 2 and 3 refer to the number of Si-O-Si bonds in which the Si atom participates. For example, the so-called T2 component refers to the component in which 2 out of the 3 Si atoms bonded to O atoms participate in Si-O-Si bonds.In unmodified colloidal silica, T2 and T3 components bonded to polyoxyethylene chains were not detected. However, in surface-modified colloidal silica according to one embodiment of the present invention, T2 and T3 components were detected. The details of this detection method are described in the examples. The surface-modified colloidal silica according to one embodiment of the present invention is a surface-modified hydrophilic colloidal silica surface modified with a surface-modifying group, thereby exhibiting affinity for water and organic solvents and possessing high dispersibility. Furthermore, it improves wettability for a wide variety of abrasive objects. Therefore, it is applicable in various fields such as CMP abrasives, inorganic fillers, inorganic binders, polymer modifiers, polymer coagulants, adsorbents, coating additives, hardening agents, antislip agents, antireflective agents for optical films, metal surface treatment agents, heat resistant agents, antistatic agents, catalyst carriers, and organosols. The following describes a polishing composition comprising surface-modified colloidal silica according to one embodiment of the present invention. [Polishing Composition] The surface-modified colloidal silica obtained by the above-described manufacturing method is suitable as abrasive grains. That is, according to a preferred embodiment of the present invention, a polishing composition is provided, comprising surface-modified colloidal silica of one embodiment of the present invention and a dispersion medium. Examples of the dispersion medium contained in the polishing composition include water and / or the organic solvents exemplified in the above-described step (synthesizing a silane coupling agent containing polyoxyethylene chains). The dispersion medium can be used alone or in combination of two or more. The surface-modified colloidal silica contained in the polishing composition of this embodiment functions as abrasive grains. The content of the surface-modified colloidal silica relative to the total mass of the polishing composition is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and particularly preferably 0.5% by mass or more. Furthermore, relative to the total mass of the grinding composition, the content of surface-modified colloidal silicon dioxide is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. That is, relative to the total mass of the grinding composition, the content of surface-modified colloidal silicon dioxide is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.2% by mass or more and 10% by mass or less, and even more preferably 0.5% by mass or more and 5% by mass or less. The grinding composition of this embodiment, without impairing the effects of the present invention, may further contain, as needed, well-known additives used in grinding compositions such as water-soluble polymers, pH adjusters, chelating agents, preservatives, and fungicides. The grinding composition of this embodiment is applicable, for example, to the grinding of monocrystalline silicon, polycrystalline silicon, silicon nitride, silicon carbonitride (SiCN), silicon oxide, metals, SiGe, resins, and other grinding objects. The object being ground can be made of only one material or a combination of two or more materials.Examples of grinding objects containing silicon oxide include TEOS-type silicon oxide (hereinafter referred to as "TEOS") produced using tetraethyl orthosilicate as a precursor, HDP (High Density Plasma) films, USG (Undoped Silicate Glass) films, PSG (Phosphorus Silicate Glass) films, BPSG (Boron-Phospho Silicate Glass) films, and RTO (Rapid Thermal Oxidation) films. Examples of the aforementioned metals include tungsten, copper, aluminum, cobalt, hafnium, nickel, gold, silver, platinum, palladium, rhodium, ruthenium, iridium, and osmium. The embodiments of the present invention have been described in detail, but this is illustrative and not limiting; clearly, the scope of the present invention should be interpreted by the appended claims. The present invention includes the following forms and configurations. 1. A surface-modified colloidal silica comprising colloidal silica and a surface-modifying group having a polyoxyethylene chain with a weight average molecular weight of 20,000 or more. 2. The surface-modified colloidal silica as described in 1. above, wherein the polyoxyethylene chain is selected from at least one group consisting of polyoxyethylene chains, polyoxypropylene chains, polyoxyethylene-polyoxypropylene chains, and polyoxyethylene-polyoxypropylene-polyoxyethylene chains. 3. The surface-modified colloidal silica as described in 1. or 2. above, wherein the polyoxyethylene chain is a polyoxyethylene chain. 4. The surface-modified colloidal silica as described in any one of 1. to 3. above, wherein the surface-modifying group comprises an aminocarbamate bond. 5. A grinding composition comprising the surface-modified colloidal silica as described in any one of 1. to 4. above and a dispersion medium. [Examples] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. Furthermore, unless otherwise specified, "%" and "parts" refer to "mass %" and "parts by mass," respectively. (Example) 150g of polyoxyethylene (PEO20,000, manufactured by Fujifilm and Hikari Pure Chemical Industries, Ltd., solid) with a weight average molecular weight (Mw) of 20,000 was added to a 1000mL sealed heat-resistant container and heated in an air bath at 80°C for 20 hours to dissolve. After 20 hours, the container was placed on a heating plate at 80°C, the lid was removed, and stirring was performed at 300rpm using a stirring blade. During stirring, 1.5g of 3-isocyanate propyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was added at a rate of 0.2g / sec. After addition, stirring was continued at 300rpm for 1 hour.The mixture was then sealed again and placed in an air bath at 80°C for 20 hours to obtain the desired surface modifier 1. Separately, 800g of a 10% by mass high-purity colloidal silica (average secondary particle size: 70nm, synthesized by sol-gel method) aqueous dispersion was collected in a 1000mL flask and heated to 60°C using a heating mantle. Once 60°C was reached, 1.5g of the aforementioned surface modifier 1 was added while stirring the aqueous dispersion at 100rpm. Furthermore, using a heating mantle, the liquid temperature was maintained at 60°C while stirring at 100rpm for 2 hours to obtain the desired surface-modified colloidal silica 1. The modification amount (content) of PEO20,000 relative to the total mass of the obtained surface-modified colloidal silica 1 was calculated to be 0.19% by mass. (Comparative Example 1) 150 g of polyoxyethylene (PEO10,000, manufactured by Merck KGaA, solid) with a weight-average molecular weight (Mw) of 10,000 was added to a 1000 mL sealed heat-resistant container and heated in an air bath at 80°C for 20 hours to dissolve. After 20 hours, the container was placed on a heating plate at 80°C, the lid was removed, and the container was stirred at 300 rpm using a stirring blade. During stirring, 3.0 g of 3-isocyanate propyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was added at a rate of 0.2 g / sec. After addition, stirring was continued at 300 rpm for 1 hour. The container was then sealed again and returned to an air bath at 80°C for 20 hours to obtain the desired surface modifier 2. In addition, 800 g of a 10% by mass high-purity colloidal silica (average secondary particle size: 70 nm, synthesized by sol-gel method) aqueous dispersion was collected in a 1000 mL flask and heated to 60°C using a heating mantle. After reaching 60°C, 0.75 g of the aforementioned surface modifier 2 was added while stirring the aqueous dispersion at 100 rpm. Then, using a heating mantle, the liquid temperature was maintained at 60°C while stirring at 100 rpm for 2 hours to obtain the desired surface-modified colloidal silica 2. The modification amount (content) of PEO10,000 relative to the total mass of the obtained surface-modified colloidal silica 2 was calculated to be 0.09% by mass. (Comparative Example 2) 21g of polyethylene glycol (PEG200, manufactured by Fujifilm and Hikari Pure Chemical Industries, Inc., liquid) with a weight-average molecular weight of 200 was added to a 1000mL sealed heat-resistant container. The container was placed on a heating plate at 80°C, the lid was removed, and the mixture was stirred at 300rpm using a stirring blade. During stirring, 20g of 3-isocyanate propyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was added at a rate of 0.2g / sec. After addition, stirring was continued at 300rpm for 1 hour. The container was then sealed again and placed in an air bath at 80°C for 20 hours to obtain the desired surface modifier 3.In addition, 800g of a high-purity colloidal silica (average secondary particle size: 70nm, synthesized by sol-gel method) aqueous dispersion with a concentration of 10% by mass was collected in a 1000mL flask and heated to 60°C using a heating mantle. After reaching 60°C, 0.03g of the surface modifier 3 obtained above was added while stirring the aqueous dispersion at 100rpm. Furthermore, using a heating mantle, the liquid temperature was maintained at 60°C while stirring at 100rpm for 2 hours to obtain the desired surface-modified colloidal silica 3. The amount of PEG200 modification (content) relative to the total mass of the obtained surface-modified colloidal silica 3 was calculated, and the result was 0.002% by mass. (Comparative Example 3) Except that the amount of surface modifier 2 added was changed to 1.5g, surface-modified colloidal silica 4 was obtained in the same manner as in Comparative Example 1. The amount (content) of PEO10,000 relative to the total mass of the obtained surface-modified colloidal silica 4 was calculated to be 0.19% by mass. (Comparative Example 4) Surface-modified colloidal silica 5 was obtained in the same manner as in Comparative Example 2, except that the amount of surface modifier 3 was changed to 3.1 g. The amount (content) of PEG200 relative to the total mass of the obtained surface-modified colloidal silica 5 was calculated to be 0.19% by mass. (Comparative Example 5) 150 g of polyoxyethylene (PEO20,000, manufactured by Fujifilm and Hikari Pure Chemical Industries Co., Ltd., solid) with a weight average molecular weight of 20,000 was added to a 250 mL sealed heat-resistant container and heated in an 80°C ambient air bath for 20 hours to dissolve. Additionally, 800 g of a 10% by mass high-purity colloidal silica (average secondary particle size: 70 nm, synthesized by sol-gel method) aqueous dispersion was collected in a 1000 mL flask and heated to 60°C using a heating mantle. Once 60°C was reached, 1.485 g of the aforementioned heated and dissolved PEG20,000 was added while stirring the aqueous dispersion at 100 rpm. This yielded the desired mixture of polyethylene glycol and colloidal silica. [Evaluation] <Structural Confirmation of Surface Modifier> The structure of the surface modifier 1 obtained above was confirmed using the following FT-IR apparatus: Apparatus used: Fourier transform infrared spectrophotometer (Spectrum 100, PerkinElmer) Detection method: ATR (Attenuated Total Reflection) method Specifically, 1 g of sample was taken from the reaction system 10 minutes after the addition of 3-isocyanate propyltrimethoxysilane from the above example. The obtained sample was placed on the ATR measuring crystal of the Spectrum 100, and the FT-IR spectrum was measured. As a result, a peak of isocyanate groups originating from the silane coupling agent was confirmed to exist near 2260 cm⁻¹.Furthermore, at the end of the reaction, a 1g sample was taken from the reaction system. The resulting sample was placed on an ATR crystal of Spectrum 100, and the FT-IR spectrum was measured. The results confirmed that the peak of the isocyanate group originating from the silane coupling agent disappeared near 2260 cm⁻¹. This confirmed that surface modifier 1, bonded by the polyoxyethylene silane coupling agent, had been formed. Also, for surface modifiers 2 and 3 obtained in Comparative Examples 1 and 2, samples were taken 10 minutes after the reaction of the silane coupling agent and again after the reaction was completed, and FT-IR measurements were performed using the same method as described above. The results confirmed that after 10 minutes, the peak of the isocyanate group originating from the silane coupling agent near 2260 cm⁻¹ disappeared after the reaction, confirming that the desired surface modifiers 2 and 3 had been formed. <Structural Confirmation of Surface-Modified Colloidal Silicon Dioxide> The structure of the surface-modified colloidal silicon dioxide was confirmed using the 29Si-NMR apparatus described below. Specifically, except for increasing the amount of silane coupling agent and polyoxyethylene in the synthesis of surface-modified colloidal silicon dioxide 1 in Example 1, two model samples for measurement were prepared in the same manner, and 29Si-NMR was measured using these model samples. Model sample B is the sample with more silane coupling agent and polyoxyethylene than model sample A. Furthermore, for comparison, unmodified colloidal silicon dioxide was also prepared. ≪29Si-NMR Apparatus≫ Spectrometer: AVANCE300 (Bruker Corporation) Observation nucleus: 29Si (resonance frequency 59.6MHz) Measurement method: CP / MAS method (Bruker Corporation, using standard pulse sequence cp.av) ・MAS conditions: 3.5kHz Waiting time: 4 seconds Contact time: 8 milliseconds Number of measurements: Model sample A: 80,000 times Model sample B: 65,536 times Unmodified colloidal silica: 4,096 times Measurement temperature: Room temperature (measured value 24°C). The 29Si-NMR measurements confirmed the presence of T2 and T3 components in both model sample A and model sample B. However, neither T2 nor T3 components were observed in the unmodified colloidal silica. Therefore, it can be confirmed that the desired surface-modified colloidal silica was obtained using the synthesis method described in this example. <Wettability> The surface-modified colloidal silica aqueous dispersions prepared in the above examples and Comparative Examples 1-3, and the mixed silica aqueous solution prepared in Comparative Example 5, were added to beakers, and silicon wafers cut into 2cm × 5cm squares were immersed for 30 seconds each. After pulling up the silicon wafers, they were wiped with a wiping cloth for 30 seconds. Then, the silicon wafers were immersed in a beaker containing pure water and washed while gently agitating for 30 seconds. After washing, the silicon wafers were pulled up, and the surface wettability was visually observed. The wettability was evaluated using the following criteria.If the rating is A, it is practical; A (Good): More than 70% of the silicon wafer remains wetted. B (Partially Poor): More than 50% but less than 70% of the silicon wafer remains wetted. C (Poor): Less than 50% of the silicon wafer remains wetted. Furthermore, the wettability of the sample in Comparative Example 4 could not be evaluated because some of it had gelled. (Stability over time) 100g each of the surface-modified colloidal silica aqueous dispersions prepared in Examples 1-4 and the mixture prepared in Comparative Example 5 were added to their respective sealed containers (100mL capacity) and allowed to stand at room temperature (25°C) for 24 hours. After 24 hours, the sedimentation state or whether the silica sol had changed into a gel was visually observed. The stability of the surface-modified colloidal silica over time was evaluated using the following criteria. If the rating is A, it is usable; A (Good): No change compared to the initial standing state; B (Slightly Poor): Some settling is observed; C (Poor): Severe settling. The following table shows the evaluation results of wettability and stability over time. [Table 1] Wettability As time goes by, stability Example A A Comparative Example 1 B A Comparative Example 2 C A Comparative Example 3 A B Comparative Example 4 Because one part of it is gelled, it cannot be evaluated. C Comparative Example 5 B A As can be seen from Table 1 above, the surface-modified colloidal silica systems of the Examples exhibit excellent wettability and stability over time. On the other hand, it can be seen that at least one property of the surface-modified colloidal silica systems of Comparative Examples 1 to 5 is poor in terms of wettability and stability over time. This application is based on Japanese Patent Application No. 2021-107392, filed on June 29, 2021, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A surface-modified colloidal silicon dioxide comprising: colloidal silicon dioxide, and a surface-modifying group having a polyoxyethylene chain having a weight average molecular weight of 20,000 to 100,000 or less; wherein the surface-modifying group comprises an aminocarbamate bond; wherein the polyoxyethylene chain is selected from at least one group formed by polyoxyethylene chains, polyoxypropylene chains, polyoxyethylene-polyoxypropylene chains, and polyoxyethylene-polyoxypropylene-polyoxyethylene chains.

2. The surface-modified colloidal silicon dioxide as claimed in claim 1, wherein the aforementioned polyoxyethylene chain is a polyoxyethylene chain.

3. A grinding composition comprising: surface-modified colloidal silicon dioxide as claimed in claim 1, and a dispersion medium.